Hello,
I just bought a eico model 625 tube tester and the guy i bought it from said that the model 625 testers don't need to be calibrated. He said to change the 6H6 tube, resistors and cap up to specs and it will work like new. For the price I paid for it, I took the chance not knowing a whole lot about tube testers in general. And for the amount of times I'll probably use it, I think it was worth the chance. But still i want to have it right so does anyone know about the eico 625 and if what guy told me was was right.
thank you

Are there any pots inside? If so, you can be sure there is some adjustment that can be made. Download the manual and see. I don't know about the 625, but on the 666 there was a calibration procedure. Since these Eicos were mostly kits, the calibration was usually pretty simple and did not require specialized instruments or precision standards. The procedure was usually at the end of the assembly instructions. Get your manual (and supplement) here:

Carmine,
The Eico 625 shares its design with a few other testers to include the Knight 600 series, which I have. In my research for the Knight I found this page, http://tubesound.com/2008/05/31/knight-600-tube-tester/ which outlines the calibration for the Knight testers. It may be applicable to your Eico.

I have an operations manual for the 625 that I got from the BAMA site but it doesn't mention anything about calibration. There's oodles of stuff out there for the 625 which you should be able to find with a little perseverance.

FYI: A tube data book for the Eico 625, dated 1978, is posted on the Archives page of this site.

Carmine,
In addition to the above information, there was also a calibration sequence published in the original Triplett 3413 parts list & diagram, giving the sequence of resistors to check and change out to obtain the general merit/value readings you want (based on your average, known good tubes). This would get done after you checked every resistor and other components for tolerances and condition. The TTT3413 and your tester are basically the same, except for the 6H6 instead of the copper oxide (meter-grade) rectifier. I could attach the Triplett diagram with the explanation in an email, but your ARF profile doesn't list your email. Most people say that these emission testers don't need calibration other than checking parts tolerances, but you can calibrate each range with this procedure...if you wanted to do that. I don't know why Eico, Heath, and Knight didn't bother to re-publish the original Triplett calibration sequence; maybe they didn't want to include a bunch of extra cal resistors or three extra trimpots in their kits.

Thanks Fred i would appreciate the info my email is TVCARM@AOL.COM The booklet that came with the tester so i am in the process of changing resistors, cap and tube. So any additional for calibration info would be appreciated. Thank you very much.
Carmine

I will try emailing to you the original Triplett 3413 pages that show the "selection" (AKA calibrating) resistors for the Line Regulation and the three range resistors. When you go to compare the Eico 625 circuit diagram to the Triplett 3413 diagram, you will notice that the Eico's R6 is the equivalent calibration resistor which can be altered to adjust the Line Regulation (which makes the applied filament-heater voltages correct when the meter's reading is at "LINE" mid-scale). R2 is the calibration resistor to fine adjust Range 1; R5 can be changed to adjust Range 2; R4 can be changed to adjust Range 3; then Range 4 should be acceptable as long as R1 (the 7 to 10W-rated 2.5K Ohm resistor) is good. It is possible that if all your tester's resistors are within tolerance, the meter's response is good (1ma/~50mv), and the 6H6 is good/stable, you may not need to change any of these "calibration" resistors....and I think alot of it depends on how picky you are & which tubes you decide to use for calibrating the ranges. Triplett (according to the engineering sheets) used "bogeys" (special labelled RMA or mfgr-supplied tubes with listed test values), which are now pretty much extinct.

...which outlines the calibration for the Knight testers. It may be applicable to your Eico.

As with most kit testers, the only "calibration" adjustment for the Knight 600 and the EICO 625 is an internal setting for the Line Adjust control. Calibration is determined by the tolerance of the parts, and the only calibration that can normally be done is replacement of out-of-tolerance parts.

Changing resistor values to affect readings on individual ranges requires a set of tubes with independently determined emission to act as calibration standards. Selecting those standard tubes is beyond the ability of most restorers. Changing resistors without those standards is futile as there is no benchmark to determine correct resistor values.

I disagree with Dale, in the sense that if one takes the time to assemble and have pretested on other, various emission-type testers (in my case I use a good TTT3414, Precision 920, Eico 666 & 667 & TTT3413, & A testers) a set of tubes, at least five to ten each for each of the four measurement ranges, good used and nos tubes, then one can calibrate an acceptable Merit/Value response for each of the four or five ranges. I've also sometimes mailed tubes around to others having similar testers, where we have compared merit readings; that can be helpful. Problem is, IMO, that to use my method does require a day or two to calibrate one tester....hardly worth the effort, considering emission testers are for only a general Bad-Good/English reading. At one time I had an offer to pickup the Triplett warehoused collection of Bogeys (several trailer loads) but had no space to store them, and after a certain age, they are no longer standards, either.

My original point was there's a resistor that can be changed for each of the 4 ranges to change the readings only for that range, if one wants to do that.

I wrote"Selecting those standard tubes is beyond the ability of most restorers. " My point stands - most restorers do not have the variety of testers and tubes that Fred has and that I have, and so cannot calibrate generate their own standard tubes.